Conductive feature formation and structure using bottom-up filling deposition

ABSTRACT

The present disclosure provides example embodiments relating to conductive features, such as metal contacts, vias, lines, etc., and methods for forming those conductive features. In some embodiments, a structure includes a first dielectric layer over a substrate, a first conductive feature through the first dielectric layer, the first conductive feature comprising a first metal, a second dielectric layer over the first dielectric layer, and a second conductive feature through the second dielectric layer having a lower convex surface extending into the first conductive feature, wherein the lower convex surface of the second conductive feature has a tip end extending laterally under a bottom boundary of the second dielectric layer.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (e.g., the number of interconnecteddevices per chip area) has generally increased while geometry size(e.g., the smallest component (or line) that can be created using afabrication process) has decreased. This scaling down process generallyprovides benefits by increasing production efficiency and loweringassociated costs.

Accompanying the scaling down of devices, manufacturers have begun usingnew and different materials and/or combination of materials tofacilitate the scaling down of devices. Scaling down, alone and incombination with new and different materials, has also led to challengesthat may not have been presented by previous generations at largergeometries.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1 through 12 are views of respective intermediate structures atrespective stages during an example method for forming conductivefeatures in accordance with some embodiments.

FIG. 13 is a flow chart of an example method for forming conductivefeatures in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Generally, the present disclosure provides example embodiments relatingto conductive features, such as metal contacts, vias, lines, etc., andmethods for forming those conductive features. An overlying conductivefeature, formed in an overlying dielectric layer, is formed to have aconvex structure to mate with a concave surface from an underlyingconductive feature. The convex structure from the overlying conductivefeature can, among other benefits, further have tip ends that assistadhering on the underlying conductive features formed in the underlyingdielectric structure where the underling conductive feature is formedin. Thus, adhesion and interface management may be better controlled.The overall contact surface area of the second conductive feature isalso increased, thus efficiently increasing electrical performance andreduce contact resistance.

Example embodiments described herein are described in the context offorming conductive features in Back End Of the Line (BEOL) and/or MiddleEnd Of the Line (MEOL) processing for a Fin Field Effect Transistor(FinFET). Other embodiments may be implemented in other contexts, suchas with different devices, such as planar Field Effect Transistors(FETs), Vertical Gate All Around (VGAA) FETs, Horizontal Gate All Around(HGAA) FETs, bipolar junction transistors (BJTs), diodes, capacitors,inductors, resistors, etc. In some instances, the conductive feature maybe part of the device, such as a plate of a capacitor or a line of aninductor. Further, some embodiments may be implemented in Front End Ofthe Line (FEOL) processing and/or for forming any conductive feature.Implementations of some aspects of the present disclosure may be used inother processes and/or in other devices.

Some variations of the example methods and structures are described. Aperson having ordinary skill in the art will readily understand othermodifications that may be made that are contemplated within the scope ofother embodiments. Although method embodiments may be described in aparticular order, various other method embodiments may be performed inany logical order and may include fewer or more steps than what isdescribed herein. In some figures, some reference numbers of componentsor features illustrated therein may be omitted to avoid obscuring othercomponents or features; this is for ease of depicting the figures.

FIGS. 1 through 12 illustrate views of respective intermediatestructures at respective stages during an example method for formingconductive features in accordance with some embodiments. FIG. 1illustrates a perspective view of an intermediate structure at a stageof the example method. The intermediate structure, as described in thefollowing, is used in the implementation of FinFETs. Other structuresmay be implemented in other example embodiments.

The intermediate structure includes first and second fins 46 formed on asemiconductor substrate 42, with respective isolation regions 44 on thesemiconductor substrate 42 between neighboring fins 46. First and seconddummy gate stacks are along respective sidewalls of and over the fins46. The first and second dummy gate stacks each include an interfacialdielectric 48, a dummy gate 50, and a mask 52.

The semiconductor substrate 42 may be or include a bulk semiconductorsubstrate, a semiconductor-on-insulator (SOI) substrate, or the like,which may be doped (e.g., with a p-type or an n-type dopant) or undoped.In some embodiments, the semiconductor material of the semiconductorsubstrate 42 may include an elemental semiconductor such as silicon (Si)or germanium (Ge); a compound semiconductor; an alloy semiconductor; ora combination thereof.

The fins 46 are formed in the semiconductor substrate 42. For example,the semiconductor substrate 42 may be etched, such as by appropriatephotolithography and etch processes, such that trenches are formedbetween neighboring pairs of fins 46 and such that the fins 46 protrudefrom the semiconductor substrate 42. Isolation regions 44 are formedwith each being in a corresponding trench. The isolation regions 44 mayinclude or be an insulating material such as an oxide (such as siliconoxide), a nitride, the like, or a combination thereof. The insulatingmaterial may then be recessed after being deposited to form theisolation regions 44. The insulating material is recessed using anacceptable etch process such that the fins 46 protrude from betweenneighboring isolation regions 44, which may, at least in part, therebydelineate the fins 46 as active areas on the semiconductor substrate 42.The fins 46 may be formed by other processes, and may includehomoepitaxial and/or heteroepitaxial structures, for example.

The dummy gate stacks are formed on the fins 46. In a replacement gateprocess as described herein, the interfacial dielectrics 48, dummy gates50, and masks 52 for the dummy gate stacks may be formed by sequentiallyforming respective layers by appropriate deposition processes, forexample, and then patterning those layers into the dummy gate stacks byappropriate photolithography and etch processes. For example, theinterfacial dielectrics 48 may include or be silicon oxide, siliconnitride, the like, or multilayers thereof. The dummy gates 50 mayinclude or be silicon (e.g., polysilicon) or another material. The masks52 may include or be silicon nitride, silicon oxynitride, silicon carbonnitride, the like, or a combination thereof.

In other examples, instead of and/or in addition to the dummy gatestacks, the gate stacks can be operational gate stacks (or moregenerally, gate structures) in a gate-first process. In a gate-firstprocess, the interfacial dielectric 48 may be a gate dielectric layer,and the dummy gate 50 may be a gate electrode. The gate dielectriclayers, gate electrodes, and masks 52 for the operational gate stacksmay be formed by sequentially forming respective layers by appropriatedeposition processes, and then patterning those layers into the gatestacks by appropriate photolithography and etch processes. For example,the gate dielectric layers may include or be silicon oxide, siliconnitride, a high-k dielectric material, the like, or multilayers thereof.A high-k dielectric material may have a k value greater than about 7.0,and may include a metal oxide of or a metal silicate of hafnium (Hf),aluminum (Al), zirconium (Zr), lanthanum (La), magnesium (Mg), barium(Ba), titanium (Ti), lead (Pb), multilayers thereof, or a combinationthereof. The gate electrodes may include or be silicon (e.g.,polysilicon, which may be doped or undoped), a metal-containing material(such as titanium, tungsten, aluminum, ruthenium, or the like), acombination thereof (such as a silicide (which may be subsequentlyformed), or multiple layers thereof. The masks 52 may include or besilicon nitride, silicon oxynitride, silicon carbon nitride, the like,or a combination thereof.

FIG. 1 further illustrates a reference cross-section that is used inlater figures. Cross-section A-A is in a plane along, e.g., channels inthe fin 46 between opposing source/drain regions. The FIGS. 2 through 12illustrate cross-sectional views at various stages of processing invarious example methods corresponding to cross-section A-A. FIG. 2illustrates a cross-sectional view of the intermediate structure of FIG.1 at the cross-section A-A.

FIG. 3 illustrates the formation of gate spacers 54, epitaxysource/drain regions 56, a contact etch stop layer (CESL) 60, and afirst interlayer dielectric (ILD) 62. Gate spacers 54 are formed alongsidewalls of the dummy gate stacks (e.g., sidewalls of the interfacialdielectrics 48, dummy gates 50, and masks 52) and over the fins 46. Thegate spacers 54 may be formed by conformally depositing, by anappropriate deposition process, one or more layers for the gate spacers54 and anisotropically etching the one or more layers, for example. Theone or more layers for the gate spacers 54 may include or be siliconoxygen carbide, silicon nitride, silicon oxynitride, silicon carbonnitride, the like, multi-layers thereof, or a combination thereof.

Recesses are then formed in the fins 46 on opposing sides of the dummygate stacks (e.g., using the dummy gate stacks and gate spacers 54 as amask) by an etch process. The etch process can be isotropic oranisotropic, or further, may be selective with respect to one or morecrystalline planes of the semiconductor substrate 42. Hence, therecesses can have various cross-sectional profiles based on the etchprocess implemented. The epitaxy source/drain regions 56 are formed inthe recesses. The epitaxy source/drain regions 56 may include or besilicon germanium, silicon carbide, silicon phosphorus, silicon carbonphosphorus, pure or substantially pure germanium, a III-V compoundsemiconductor, a II-VI compound semiconductor, or the like. The epitaxysource/drain regions 56 may be formed in the recesses by an appropriateepitaxial growth or deposition process. In some examples, epitaxysource/drain regions 56 can be raised with respect to the fin 46, andcan have facets, which may correspond to crystalline planes of thesemiconductor substrate 42.

A person having ordinary skill in the art will also readily understandthat the recessing and epitaxial growth may be omitted, and thatsource/drain regions may be formed by implanting dopants into the fins46 using the dummy gate stacks and gate spacers 54 as masks. In someexamples where epitaxy source/drain regions 56 are implemented, theepitaxy source/drain regions 56 may also be doped, such as by in situdoping during epitaxial growth and/or by implanting dopants into theepitaxy source/drain regions 56 after epitaxial growth. Hence, asource/drain region may be delineated by doping (e.g., by implantationand/or in situ during epitaxial growth, if appropriate) and/or byepitaxial growth, if appropriate, which may further delineate the activearea in which the source/drain region is delineated.

The CESL 60 is conformally deposited, by an appropriate depositionprocess, on surfaces of the epitaxy source/drain regions 56, sidewallsand top surfaces of the gate spacers 54, top surfaces of the masks 52,and top surfaces of the isolation regions 44. Generally, an etch stoplayer (ESL) can provide a mechanism to stop an etch process whenforming, e.g., contacts or vias. An ESL may be formed of a dielectricmaterial having a different etch selectivity from adjacent layers orcomponents. The CESL 60 may comprise or be silicon nitride, siliconcarbon nitride, silicon carbon oxide, carbon nitride, the like, or acombination thereof.

The first ILD 62 is deposited, by an appropriate deposition process, onthe CESL 60. The first ILD 62 may comprise or be silicon dioxide, alow-k dielectric material (e.g., a material having a dielectric constantlower than silicon dioxide), silicon oxynitride, phosphosilicate glass(PSG), borosilicate glass (BSG), borophosphosilicate glass (BPSG),undoped silicate glass (USG), fluorinated silicate glass (FSG),organosilicate glasses (OSG), SiO_(x)C_(y), Spin-On-Glass,Spin-On-Polymers, silicon carbon material, a compound thereof, acomposite thereof, the like, or a combination thereof.

The first ILD 62 may be planarized after being deposited, such as by achemical mechanical planarization (CMP). In a gate-first process, a topsurface of the first ILD 62 may be above the upper portions of the CESL60 and the gate stacks, and processing described below with respect toFIGS. 4 and 5 may be omitted. Hence, the upper portions of the CESL 60and first ILD 62 may remain over the gate stacks.

FIG. 4 illustrates the replacement of the dummy gate stacks withreplacement gate structures. The first ILD 62 and CESL 60 are formedwith top surfaces coplanar with top surfaces of the dummy gates 50. Aplanarization process, such as a CMP, may be performed to level the topsurfaces of the first ILD 62 and CESL 60 with the top surfaces of thedummy gates 50. The CMP may also remove the masks 52 (and, in someinstances, upper portions of the gate spacers 54) on the dummy gates 50.Accordingly, top surfaces of the dummy gates 50 are exposed through thefirst ILD 62 and the CESL 60.

With the dummy gates 50 exposed through the first ILD 62 and the CESL60, the dummy gates 50 are removed, such as by one or more etchprocesses. The dummy gates 50 may be removed by an etch processselective to the dummy gates 50, wherein the interfacial dielectrics 48act as ESLs, and subsequently, the interfacial dielectrics 48 canoptionally be removed by a different etch process selective to theinterfacial dielectrics 48. Recesses are formed between gate spacers 54where the dummy gate stacks are removed, and channel regions of the fins46 are exposed through the recesses.

The replacement gate structures are formed in the recesses where thedummy gate stacks were removed. The replacement gate structures eachinclude, as illustrated, an interfacial dielectric 70, a gate dielectriclayer 72, one or more optional conformal layers 74, and a gateconductive fill material 76. The interfacial dielectric 70 is formed onsidewalls and top surfaces of the fins 46 along the channel regions. Theinterfacial dielectric 70 can be, for example, the interfacialdielectric 48 if not removed, an oxide (e.g., silicon oxide) formed bythermal or chemical oxidation of the fin 46, and/or an oxide (e.g.,silicon oxide), nitride (e.g., silicon nitride), and/or anotherdielectric layer.

The gate dielectric layer 72 can be conformally deposited in therecesses where dummy gate stacks were removed (e.g., on top surfaces ofthe isolation regions 44, on the interfacial dielectric 70, andsidewalls of the gate spacers 54) and on the top surfaces of the firstILD 62, the CESL 60, and gate spacers 54. The gate dielectric layer 72can be or include silicon oxide, silicon nitride, a high-k dielectricmaterial (examples of which are provided above), multilayers thereof, orother dielectric material.

Then, the one or more optional conformal layers 74 can be conformally(and sequentially, if more than one) deposited on the gate dielectriclayer 72. The one or more optional conformal layers 74 can include oneor more barrier and/or capping layers and one or more work-functiontuning layers. The one or more barrier and/or capping layers can includea nitride, silicon nitride, carbon nitride, and/or aluminum nitride oftantalum and/or titanium; a nitride, carbon nitride, and/or carbide oftungsten; the like; or a combination thereof. The one or morework-function tuning layer may include or be a nitride, silicon nitride,carbon nitride, aluminum nitride, aluminum oxide, and/or aluminumcarbide of titanium and/or tantalum; a nitride, carbon nitride, and/orcarbide of tungsten; cobalt; platinum; the like; or a combinationthereof.

A layer for the gate conductive fill material 76 is formed over the oneor more optional conformal layers 74 (e.g., over the one or morework-function tuning layers), if implemented, and/or the gate dielectriclayer 72. The layer for the gate conductive fill material 76 can fillremaining recesses where the dummy gate stacks were removed. The layerfor the gate conductive fill material 76 may be or comprise ametal-containing material such as tungsten, cobalt, aluminum, ruthenium,copper, multi-layers thereof, a combination thereof, or the like.Portions of the layer for the gate conductive fill material 76, one ormore optional conformal layers 74, and gate dielectric layer 72 abovethe top surfaces of the first ILD 62, the CESL 60, and gate spacers 54are removed, such as by a CMP. The replacement gate structurescomprising the gate conductive fill material 76, one or more optionalconformal layers 74, gate dielectric layer 72, and interfacialdielectric 70 may therefore be formed as illustrated in FIG. 4.

FIG. 5 illustrates the formation of a second ILD 80 over the first ILD62, CESL 60, gate spacers 54, and replacement gate structures. Althoughnot illustrated, in some examples, an ESL may be deposited over thefirst ILD 62, etc., and the second ILD 80 may be deposited over the ESL.If implemented, the ESL may comprise or be silicon nitride, siliconcarbon nitride, silicon carbon oxide, carbon nitride, the like, or acombination thereof. The second ILD 80 may comprise or be silicondioxide, a low-k dielectric material, silicon oxynitride, PSG, BSG,BPSG, USG, FSG, OSG, SiO_(x)C_(y), Spin-On-Glass, Spin-On-Polymers,silicon carbon material, a compound thereof, a composite thereof, thelike, or a combination thereof.

FIG. 6 illustrates the formation of respective openings 82 and 84through the second ILD 80, the first ILD 62, and the CESL 60 to exposeat least a portion of an epitaxy source/drain region 56, and through thesecond ILD 80 to expose at least a portion of a replacement gatestructure. The second ILD 80, the first ILD 62, and the CESL 60 may bepatterned with the openings 82 and 84, for example, usingphotolithography and one or more etch processes.

FIG. 7 illustrates the formation of conductive features 90 and 92 in theopenings 82 and 84 to the epitaxy source/drain region 56 and to thereplacement gate structure, respectively. The conductive feature 90includes, in the illustrated example, an adhesion layer 94, a barrierlayer 96 on the adhesion layer 94, a silicide region 98 on the epitaxysource/drain region 56, and a conductive fill material 100 on thebarrier layer 96, for example. The conductive feature 92 includes, inthe illustrated example, an adhesion layer 94, a barrier layer 96 on theadhesion layer 94, and conductive fill material 100 on the barrier layer96, for example.

The adhesion layer 94 can be conformally deposited in the openings 82and 84 (e.g., on sidewalls of the openings 82 and 84, exposed surface ofthe epitaxy source/drain region 56, and exposed surface of thereplacement gate structure) and over the second ILD 80. The adhesionlayer 94 may be or comprise titanium, tantalum, the like, or acombination thereof, and may be deposited by atomic layer deposition(ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD),or another deposition technique. The barrier layer 96 can be conformallydeposited on the adhesion layer 94, such as in the openings 82 and 84and over the second ILD 80. The barrier layer 96 may be or comprisetitanium nitride, titanium oxide, tantalum nitride, tantalum oxide, thelike, or a combination thereof, and may be deposited by ALD, CVD, oranother deposition technique. In some examples, at least a portion ofthe adhesion layer 94 can be treated to form the barrier layer 96. Forexample, a nitridation process, such as including a nitrogen plasmaprocess, can be performed on the adhesion layer 94 to convert at leastthe portion of the adhesion layer 94 into the barrier layer 96. In someexamples, the adhesion layer 94 can be completely converted such that noadhesion layer 94 remains and the barrier layer 96 is anadhesion/barrier layer, while in other examples, a portion of theadhesion layer 94 remains unconverted such that the portion of theadhesion layer 94 remains with the barrier layer 96 on the adhesionlayer 94.

Silicide region 98 may be formed on the epitaxy source/drain region 56by reacting an upper portion of the epitaxy source/drain region 56 withthe adhesion layer 94, and possibly, the barrier layer 96. An anneal canbe performed to facilitate the reaction of the epitaxy source/drainregion 56 with the adhesion layer 94 and/or barrier layer 96.

The conductive fill material 100 can be deposited on the barrier layer96 and fill the openings 82 and 84. The conductive fill material 100 maybe or comprise cobalt, tungsten, copper, ruthenium, aluminum, gold,silver, alloys thereof, the like, or a combination thereof, and may bedeposited by CVD, ALD, PVD, or another deposition technique. After theconductive fill material 100 is deposited, excess conductive fillmaterial 100, barrier layer 96, and adhesion layer 94 may be removed byusing a planarization process, such as a CMP, for example. Theplanarization process may remove excess conductive fill material 100,barrier layer 96, and adhesion layer 94 from above a top surface of thesecond ILD 80. Hence, top surfaces of the conductive features 90 and 92and the second ILD 80 may be coplanar. The conductive features 90 and 92may be or may be referred to as contacts, plugs, etc.

Although FIGS. 6 and 7 illustrate the conductive feature 90 to theepitaxy source/drain region 56 and the conductive feature 92 to thereplacement gate structure being formed simultaneously, the respectiveconductive features 90 and 92 may be formed separately and sequentially.For example, the opening 82 to the epitaxy source/drain region 56 may befirst formed, as in FIG. 6 and filled to form the conductive feature 90to the epitaxy source/drain region 56, as in FIG. 7. Then, the opening84 to the replacement gate structure may be formed, as in FIG. 6, andfilled to form the conductive feature 92 to the replacement gatestructure, as in FIG. 7. Another order of processing may be implemented.

FIG. 8 illustrates the formation of an ESL 110 and an intermetallizationdielectric (IMD) 112 over the ESL 110. The ESL 110 is deposited on topsurfaces of the second ILD 80 and conductive features 90 and 92. The ESL110 may comprise or be silicon nitride, silicon carbon nitride, siliconcarbon oxide, carbon nitride, the like, or a combination thereof, andmay be deposited by CVD, plasma enhanced CVD (PECVD), ALD, or anotherdeposition technique. The IMD 112 may comprise or be silicon dioxide, alow-k dielectric material, silicon oxynitride, PSG, BSG, BPSG, USG, FSG,OSG, SiO_(x)C_(y), Spin-On-Glass, Spin-On-Polymers, silicon carbonmaterial, a compound thereof, a composite thereof, the like, or acombination thereof. The IMD 112 may be deposited by spin-on, CVD,flowable CVD (FCVD), PECVD, PVD, or another deposition technique. Athickness of the ESL 110 can be in a range from about 10 nm to about 500nm, and a thickness of the IMD 112 can be in a range from about 50 nm toabout 800 nm. A combined thickness of the IMD 112 and ESL 110 can be ina range from about 100 nm to about 1000 nm.

FIG. 9 illustrates the formation of openings 120 and 122 to theconductive features 90 and 92, respectively, through the IMD 112 and ESL110. The IMD 112 and ESL 110 may be patterned with the openings 120 and122, for example, using photolithography and one or more etch processes.The etch process may include a reactive ion etch (RIE), neutral beametch (NBE), inductively coupled plasma (ICP) etch, capacitively coupledplasma CCP etch, ion beam etch (IBE), the like, or a combinationthereof. The etch process may be anisotropic. In some examples, theetching process can include a plasma using a first gas comprising carbontetrafluoride (CF4), hexafluoroethane (C2F6), octafluoropropane (C3F8),fluoroform (CHF3), difluoromethane (CH2F2), fluoromethane (CH3F), acarbon fluoride (e.g., CxFy where x can be in a range from 1 to 5 and ycan be in a range from 4 to 8), the like, or a combination thereof. Theplasma can further use a second gas comprising nitrogen (N2), hydrogen(H2), oxygen (O2), argon (Ar), xenon (Xe), helium (He), carbon monoxide(CO), carbon dioxide (CO2), carbonyl sulfide (COS), the like, or acombination thereof. An inert gas may be optionally supplied during theetching process. In some examples, a ratio of the flow rate of the firstgas to the flow rate of the second gas can be in a range from about1:1000 to about 1000:1, such as from about 1:10 to about 10:1. Apressure of the plasma etch can be in a range from about 0.1 mTorr toabout 100 mTorr. A power of the plasma generator for the plasma etch canbe in a range from about 30 W to about 5000 W. A frequency of the plasmagenerator for the plasma etch can be about 40 KHz, about 2 MHz, or fromabout 12 MHz to about 100 MHz, such as about 13.56 MHz. A substrate biasvoltage of the plasma etch can be in a range from about 10 kV to about100 kV and with a duty cycle in a range from about 5% to about 95%.

FIG. 10 illustrates the formation of recesses 202, 201 in the conductivefeatures 90 and 92 and formed through the openings 120 and 122 to theconductive features 90 and 92, respectively, through the IMD 112 and ESL110. After the openings 120, 122 are formed, a wet cleaning process maybe performed to remove residuals as well as native oxides from theconductive features 90, 92. The residuals may come from the etchingbyproduct while forming the openings 120, 122 in the previous operationsteps. The residuals may also come from the environment whentransferring the substrate between different processing chambers whileforming the IMD 112 and ESL 110. Furthermore, native oxides are oftenformed on the surfaces of the conductive features 90, 92. The wetcleaning process is performed to efficiently remove the residuals aswell as the native oxides from the conductive features 90, 92.Furthermore, the wet cleaning process also etches the surface of theconductive features 90, 92 to form the recesses 202, 201 on the surfaceof the conductive features 90, 92 after the residuals and/or nativeoxide are removed therefrom.

In an example, the wet cleaning process can include immersing thesemiconductor substrate 42 in deionized (DI) water or another suitablechemical (which may be diluted in DI water). It is believed that DIwater may react with the native oxide grown on the surface of theconductive features 90, 92. In the example wherein the conductivefeatures 90, 92 are fabricated from Co containing materials, DI watermay efficiently react with CoO_(x), thus removing the native oxide(e.g., CoO_(x)) along with a portion of the Co thereunder, forming therecesses 202, 201 on the conductive features 90, 92. The recesses 202,201 may be formed as a concave surface (e.g., an upper concave surfaceon the conductive features 90, 92) having tip ends 203, 205 (as shown inthe recess 202) formed under a bottom surface of the ESL 110. As the wetcleaning process is an isotropic etching process, the chemical reactionbetween the solution and the conductive features 90, 92 isotropicallyand continuously occurs when the solution contacts the conductivefeatures 90, 92 until a predetermined process time period is reached. Itis believed that the tip ends 203, 205 of the recesses 202 extendlaterally from the conductive features 90, 92 and further extendunderneath the bottom surface of the ESL 110. The tip ends 203, 205 mayassist the materials subsequently formed therein to anchor and engage inthe openings 120, 122 with better adhesion and clinch.

After the DI water cleaning, the semiconductor substrate 42 may furtherbe optionally cleaned in a solution including other chemicals in DIwater. Suitable examples of the chemicals include acid chemicals, suchas citric acid, or a mixture of acid chemicals. The chemicals in the DIwater may have a concentration from about 0.1% to about 20% by volume.The solution, during the immersion, may be at a temperature in a rangefrom about 20° C. to about 90° C. The semiconductor substrate 42 may beimmersed in the solution for a duration in a range from about 5 secondsto about 120 seconds to form the recesses 202, 201. After the cleaning,the recesses 202, 201 may have a depth 225 (see FIG. 12) from the top(e.g., horizontal) surface of the second ILD 80 in a range greater than15 Å, such as from about 20 Å to about 100 Å, and more particularly,such as from about 30 Å to about 50 Å, although other depths may beachieved. The semiconductor substrate 42 may optionally be rinsed inisopropyl alcohol (IPA) following the immersion in the solution to drythe semiconductor substrate 42.

FIG. 11 illustrates the partial formation of second conductive features204, 206 in the openings 120 and 122, respectively, in connection withthe conductive features 90, 92. The second conductive features 204, 206are formed in the recesses 202, 201 on the surface of the conductivefeatures 90, 92, filling the recesses 202, 201 and forming the secondconductive features 204, 206 in a bottom-up manner for filling theopenings 120, 122.

By forming the second conductive features 204, 206 in a bottom-upmanner, the second conductive features 204, 206 may be grown from thebottom surface, e.g., from the recesses 202, 201, to slowly andgradually grow the second conductive features 204, 206 predominatelyfrom the bottom, until a desired thickness/depth of the secondconductive features 204, 206 is reached in the openings 120, 122. As aresult, undesired defects, such as voids or seams, may be eliminated asthe likelihood of forming the early closure of the openings 120, 122 orlateral growth in the openings 120, 122 is much reduced. Thus, thebottom-up deposition process assists forming the second conductivefeatures as a seam-free (or void free) structure.

In an example, the second conductive features 204, 206 can be depositedin the openings 120, 122 by CVD, ALD, electroless deposition (ELD), PVD,electroplating, or another deposition technique. In a specific example,the second conductive features 204, 206 are formed by a thermal CVDprocess, without plasma generated during the deposition process. It isbelieved that a thermal CVD process may provide thermal energy to assistforming nucleation sites for forming the second conductive features 204,206. The thermal energy provided from the thermal CVD process maypromote incubation of the nucleation sites at a relatively long periodof time. As the deposition rate is controlled at a relatively lowdeposition rate, such as less than 15 Å per second, the slow growingprocess allows the nucleation sites to slowly grow into the secondconductive features 204, 206. The low deposition rate may be controlledby supplying a deposition gas mixture with a relatively low metalprecursor ratio in a hydrogen dilution gas mixture, which will bedescribed detail below. The nucleation sites are prone to form atcertain locations of the substrate having similar material properties tothe nucleation sites. For example, as the nucleation sites includesmetal materials for forming the second conductive features 204, 206, thenucleation sites are then prone to adhere and nucleate on the metalmaterials (e.g., the first conductive features 90, 92) on the substrate.Once the nucleation sites are formed at the selected locations, theelements/atoms may then continue to adhere and anchor on the nucleationsites, piling up the elements/atoms at the selected locations, of thesubstrate, providing a selective deposition process, as well asbottom-up deposition process, is obtained. In the example depicted inFIG. 11, the nucleation sites are selectively incubated at certainlocations (e.g., in the recesses 202, 201 above the first conductivefeatures 90, 92) in the openings 120, 122, so that the second conductivefeatures 204, 206 may grow from the recesses 202, 201 vertically fromthe bottom upward to fill in the openings 120, 122.

The second conductive features 204, 206 may be or comprise tungsten,cobalt, copper, ruthenium, aluminum, gold, silver, alloys thereof, thelike, or a combination thereof. FIG. 11 depicts that the secondconductive features 204, 206 partially fill the openings 120, 122 forease of explanation of the bottom-up deposition process as thedeposition process is not yet finished or terminated. When the secondconductive features 204, 206 substantially fill the openings 120, 122,to form the completed second conductive feature 207, 208, the depositionprocess is then terminated, as shown in FIG. 12. As the secondconductive features 207, 208 grow on the first conductive features 90,92 and fill the recesses 202, 201, the resultant second conductivefeatures 207, 208 may have a bottom portion having a substantiallyrounded and/or convex structure 222 (filling the concave surface fromthe recesses 202, 201 with the depth 225). The convex structure 222extends laterally and outward below the ESL 110 and the below the top(e.g., horizontal) surface of the second ILD 80. The convex structure222 has the depth 225 (e.g., the same depth from the concave surfacefrom the recesses 202, 201) in a range greater than 15 Å, such as fromabout 20 Å to about 100 Å, and more particularly, such as from about 30Å to about 50 Å, although other depths may be achieved. After theresultant second conductive features 207, 208 fill the recesses 202,201, the second conductive feature 207, 208 include the tip ends 203,205, respectively. The tip ends 203, 205 are in direct contact with thebottom surface of the ESL 110, as shown in the magnified view 240 inFIG. 12, having a width 250 in a range from 1 nm to about 5 nm.

The excess second conductive feature 207, 208 outgrown from the openings120, 122 may be removed by using a planarization process, such as a CMP,for example. The planarization process may remove excess secondconductive feature 207, 208 from above a top surface of the IMD 112.Hence, top surfaces of the second conductive feature 207, 208 and theIMD 112 may be coplanar. The second conductive feature 207, 208 may beor may be referred to as contacts, plugs, conductive lines, conductivepads, vias, etc.

Furthermore, the better interface management provided by the convexstructure 222 and the tip ends 203, 205 may also prevent the secondconductive features 207, 208 from undesirably pulling back at thesubsequent CMP process.

In some examples, a barrier and/or adhesion layer is eliminated in theopenings 120 and 122 before the second conductive feature 207, 208 isdeposited in the openings 120 and 122. Since the examples depicted inFIGS. 11 and 12 show a bottom-up deposition process, a barrier and/oradhesion layer may be eliminated as the second conductive feature 207,208 may be directly grown in the recesses 201, 202 from the underlyingconductive features 90, 92 by forming the nucleation sites thereon withslow incubation. In some examples, different integration schemes, suchas additional interface layers or bottom layers, may be utilized whendifferent metal materials are used for conductive features 207, 208.Furthermore, as discussed above, the tip ends 203, 205 formed in therecesses 201, 202 also assist the mechanical attachment (e.g., ananchor-like stress and/or clinch) of the second conductive feature 207,208 in the recesses 201, 202 to the underlying conductive features 90,92, thus promoting interface adhesion and integration. Furthermore, asthe conductive materials from the second conductive feature 207, 208further extend downward to the conductive features 90, 92 at theinterface where the convex structure 222 mated with the concave surfacefrom the conductive features 90, 92, the overall surface contact area ofthe second conductive feature 207, 208 in the openings 120, 122 isincreased, thus increasing the overall conductive contact surface area,promoting electrical performance and lower interface/contact resistance.

In an example, the bottom-up thermal chemical deposition process may beobtained by controlling a process pressure less than about 150 Torr,such as from about 5 Torr to about 100 Torr, for example about 20 Torr.The process temperature may be controlled in a range from about 200degrees Celsius to about 400 degrees Celsius. A deposition gas mixtureincluding at least a metal precursor and a reacting gas is used. In aspecific example, the metal precursor is a tungsten containing precursorwhen the second conductive feature 207, 208 is a tungsten containingmaterial. Suitable examples of the metal precursor material includesWF₆, WCl_(x)R_(1-x), W(CO)₆ and the like. In an example, the depositiongas mixture includes WF₆. Other reacting gas, such as H₂, N₂, NH₃ andthe like may also be supplied in the deposition gas mixture. In aspecific example, the deposition gas mixture includes WF₆ and H₂. Thereacting gas and the metal precursor may be supplied in the depositiongas mixture at a ratio greater than 20. For example, the WF₆ and H₂ maybe supplied at a hydrogen gas dilution process. For example, the flowamount by volume of H₂ gas supplied in the deposition gas mixture isgreater than WF₆ gas flow amount by volume. The flow amount by volume ofH₂ gas is at least about 20 times greater than the flow amount by volumeof WF₆ gas (e.g., H₂/WF₆>20). In a specific example, a ratio of the flowamount by volume of H₂ gas to the flow amount by volume of WF₆ gas isfrom about 30 to about 150, such as from about 40 to about 120. The RFsource or bias power is not turned on and/or may not be necessary whilesupplying the deposition gas mixture. Thus, the deposition process canbe a plasma free deposition process.

FIG. 13 is a flow chart of an example method for forming conductivefeatures in accordance with some embodiments. In operation 502, a firstconductive feature is formed in a first dielectric layer. An example ofoperation 502 is illustrated in and described with respect to FIGS. 6and 7. For example, the conductive feature 90 is formed in the secondILD 80, the first ILD 62, and CESL 60.

In operation 504, a second dielectric layer is formed over the firstconductive feature and the first dielectric layer. An example ofoperation 504 is illustrated in and described with respect to FIG. 8.For example, the ESL 110 and IMD 112 are formed over the conductivefeature 90 and the second ILD 80, the first ILD 62, and CESL 60.

In operation 506, an opening is formed through the second dielectriclayer to the first conductive feature. An example of operation 506 isillustrated in and described with respect to FIG. 9. For example, theopening 120 is formed through the ESL 110 and IMD 112 to the conductivefeature 90.

In operation 508, a recess is formed in the first conductive featureexposed through the opening through the second dielectric layer. Anexample of operation 508 is illustrated in and described with respect toFIG. 10. For example, the recess 201 is formed in the conductive feature90 exposed through the opening 120.

In operation 510, a second conductive feature is formed in the openingthrough the second dielectric layer and filling the recesses andcontacting the underlying first conductive feature. The secondconductive feature is formed by a bottom-up process without assistanceof a barrier/adhesion layer at the interface where the second conductivefeature is formed and grown on. An example of operation 510 isillustrated in and described with respect to FIGS. 11-12. For example,the second conductive feature 208 is formed in the opening 120 fillingthe recess 201 and contacting the first conductive feature 90.

Thus, by utilizing recesses formed between the first conductive featuresand the second conductive feature and filled by the conductive fillmaterial, a better interface management and electrical properties may beobtained. Furthermore, the bottom-up deposition process of the secondconductive feature may also assist forming the second conductive featuredirectly in contact with the underlying conductive features through therecesses without barrier layer/adhesion layer formed at the interfaceand sidewall, so better manufacturing control and device structures andperformance may be obtained and achieved.

In an embodiment, a structure includes a first dielectric layer over asubstrate, a first conductive feature through the first dielectriclayer, the first conductive feature comprising a first metal, a seconddielectric layer over the first dielectric layer, and a secondconductive feature through the second dielectric layer having a lowerconvex surface extending into the first conductive feature, wherein thelower convex surface of the second conductive feature has a tip endextending laterally under a bottom boundary of the second dielectriclayer. In an embodiment, the second conductive feature is in directcontact with the second dielectric layer. In an embodiment, the seconddielectric layer includes an etching stop layer. In an embodiment, thetip end is in direct contact with a bottom surface of the etching stoplayer. In an embodiment, the tip end has a width in a range from 1 nmand about 5 nm. In an embodiment, the lower convex surface has a depthof greater than 15 Å. In an embodiment, the second conductive featureincludes a second metal different from the first metal. In anembodiment, the second conductive feature is a seam-free structure. Inan embodiment, the first conductive feature includes cobalt, and thesecond conductive feature includes tungsten.

In another embodiment, a method includes forming a first conductivefeature in a first dielectric layer, forming a concave surface on thefirst conductive feature, and forming a second conductive feature in asecond dielectric layer. The second dielectric layer is over the firstdielectric layer. The second conductive feature has a convex surfacemating with the concave surface of the first conductive feature. Theconvex surface of the second conductive feature has a tip end extendinglaterally under a bottom surface of the second dielectric layer. In anembodiment, the convex surface has a depth greater than 15 Å. In anembodiment, the second conductive feature is formed by a bottom-updeposition process. In an embodiment, the bottom-up deposition processfurther includes supplying a deposition gas mixture including a metalcontaining gas and a reacting gas, and maintaining a process pressureless than 150 Torr. In an embodiment, a ratio of respective flow ratesof the reacting gas to the metal containing gas is greater than 20. Inan embodiment, the bottom-up deposition process is a plasma free thermalCVD process. In an embodiment, the concave surface of the firstconductive feature is formed by a wet cleaning process. In anembodiment, the second conductive feature is in direct contact with thesecond dielectric layer without a barrier layer or an adhesion layertherebetween.

In yet another embodiment, a method for semiconductor processingincludes forming a concave surface on a first conductive feature in afirst dielectric layer by performing an isotropic etching processthrough a second dielectric layer, the second dielectric layer is overthe first dielectric layer, and forming a second conductive feature inthe second dielectric layer using a bottom-up deposition process. Thesecond conductive feature having a convex surface mating with theconcave surface on the first conductive feature. The convex surface ofthe second conductive feature has a tip end extending laterally under abottom surface of the second dielectric layer. In an embodiment, thesecond conductive feature is formed without plasma. In an embodiment,the wet solution removes a native oxide from the first conductivefeature to form the concave surface.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for semiconductor processing, the methodcomprising: forming a first conductive feature in a first dielectriclayer; forming a concave surface on the first conductive feature, theconcave surface extends continuously from a first sidewall of aconductive barrier layer of the first conductive feature to a secondsidewall of the conductive barrier layer of the first conductivefeature; and forming a second conductive feature in a second dielectriclayer, the second dielectric layer being over the first dielectriclayer, the second conductive feature having a convex surface mating withthe concave surface of the first conductive feature, wherein the convexsurface of the second conductive feature has a tip end extendinglaterally under a bottom surface of the second dielectric layer.
 2. Themethod of claim 1, wherein the convex surface has a depth greater than15 Å.
 3. The method of claim 1, wherein the second conductive feature isformed by a bottom-up deposition process.
 4. The method of claim 3,wherein the bottom-up deposition process further comprises: supplying adeposition gas mixture including a metal containing gas and a reactinggas; and maintaining a process pressure less than 150 Torr.
 5. Themethod of claim 4, wherein a ratio of respective flow rates of thereacting gas to the metal containing gas is greater than
 20. 6. Themethod of claim 3, wherein the bottom-up deposition process is a plasmafree thermal CVD process.
 7. The method of claim 1, wherein the concavesurface of the first conductive feature is formed by a wet cleaningprocess.
 8. The method of claim 1, wherein the second conductive featureis in direct contact with the second dielectric layer without a barrierlayer or an adhesion layer therebetween.
 9. A method for semiconductorprocessing, the method comprising: forming a concave surface on a firstconductive feature in a first dielectric layer by performing anisotropic etching process through a second dielectric layer, wherein theconcave surface extends continuously from a first sidewall of aconductive barrier layer of the first conductive feature to a secondsidewall of the conductive barrier layer of the first conductivefeature, and wherein the second dielectric layer is over the firstdielectric layer; and forming a second conductive feature in the seconddielectric layer using a bottom-up deposition process, the secondconductive feature having a convex surface mating with the concavesurface on the first conductive feature, wherein the convex surface ofthe second conductive feature has a tip end extending laterally under abottom surface of the second dielectric layer.
 10. The method of claim9, wherein the second conductive feature is formed without plasma. 11.The method of claim 9, wherein the isotropic etching process includes awet etching process using a wet solution, wherein the wet solutionremoves a native oxide from the first conductive feature to form theconcave surface.
 12. A method comprising: forming a first conductivefeature extending through a first dielectric layer; depositing a seconddielectric layer over the first conductive feature and the firstdielectric layer; patterning an opening in the second dielectric layerto expose the first conductive feature; etching the first conductivefeature to extend the opening below a bottommost surface of the seconddielectric layer, wherein etching the first conductive feature comprisesimmersing the first conductive feature in a solution comprisingdeionized (DI) water, wherein after etching the first conductivefeature, a top surface of the first conductive feature extends directlyunder the bottommost surface of the second dielectric layer; and forminga second conductive feature through the second dielectric layer andelectrically connected to the first conductive feature, wherein formingthe second conductive feature comprises depositing a portion of thesecond conductive feature to extend continuously between the top surfaceof the first conductive feature and the bottommost surface of the seconddielectric layer.
 13. The method of claim 12, wherein the secondconductive feature has a same material composition throughout, andwherein forming the second conductive feature comprises completelyfilling the opening with the second conductive feature.
 14. The methodof claim 12, wherein forming the second conductive feature comprisesusing a bottom-up deposition process.
 15. The method of claim 12,wherein depositing the second dielectric layer comprises: depositing anetch stop layer contacting the first dielectric layer and the firstconductive feature; and depositing a low-k dielectric layer over theetch stop layer.
 16. The method of claim 12, wherein etching the firstconductive feature comprises removing a native oxide portion of thefirst conductive feature.
 17. The method of claim 12, wherein the firstconductive feature and the second conductive feature comprise differentmaterials.
 18. The method of claim 17, wherein the first conductivefeature comprises cobalt, and wherein second conductive featurecomprises tungsten.
 19. The method of claim 12, wherein forming thesecond conductive feature comprises a plasma free deposition process.20. The method of claim 12, wherein immersing the first conductivefeature in the solution comprising DI water removes a native oxide on asurface of the first conductive feature exposed by the opening to definethe top surface of the first conductive feature extending directly underthe bottommost surface of the second dielectric layer.